Variable attenuators are used in a host of applications wherever a signal power level variation and reduction is desired. A number of such applications include communication system and devices, such as wireless area network systems, mobile communication devices, global positioning system (GPS) receivers, and the like. For example, in transmitters including wireless transmitters, in situations where a lower transmit power is sufficient to maintain a communication link, decreasing the output power level may be desired in order to prevent saturating receivers in the vicinity of the transmitter with a high power transmission signal. On the other hand, in receivers, when the input received signal is too high and can potentially saturate some building blocks down in the receive chain, an attenuator may be applied to lower the signal level, and relax the linearity specification on the following building blocks.
Existing solutions are provided in a number of topologies, for example, current commuting variable gain amplifiers (VGAs), CMOS hybrid-pi attenuators, variable resistance load amplifiers (e.g., with a shunt FET), and reflection-type attenuators such as low-phase-shift and varactor diode type attenuators. The existing solutions, although may work for their objective applications, exhibit a number of shortcomings in addressing desired linearity, noise performance, high frequency operation, and providing matched input and output ports.